Example of radioisotope dating
Because lead (the stable daughter of uranium) has a very different arrangement of electrons, it does not make its way into the crystal as it is forming.The formation of crystals in the magma marks the moment that the radio-isotopic clock starts ticking.Radioactive decay Radioisotopic dating relies on the process of radioactive decay, in which the nuclei of radioactive atoms emit particles.
The example above describes uranium/lead decay, which happens very slowly; however, different radioactive elements have different half-lives. This allows scientists to date events that are more or less ancient.
To see how it works, we'll start at the beginning, using uranium as an example: At left, a zircon crystal in a thin section cut from granite. Crystal structure image adapted fromadapted from Materialscientist CC Attribution-Share Alike 3.0 Unported Tens to hundreds of thousands of years before a major volcanic eruption, magma builds up beneath the surface of the Earth.
In the magma, crystals of zirconium silicate (called zircons), as well as other crystals, form.
However, to read any clock accurately we must know where the clock was set at the beginning.
Most people think that radioactive dating has proven the earth is billions of years old.